Probability:

Basically probability is a subject that deals with uncertainty. It is the likelihood that a particular event will occur. Probability values are assigned on a scale from 0 to 1, with values near 0 indicating that an event is unlikely to occur and those near 1 indicating that an event is likely to take place.
In simple words probability is the ratio of "the number of ways the outcome may occur" to "the number of total possible outcomes" for that event. Probability is expressed as a fraction or decimal.

Example:
1) Suppose there are 12 balls in a bag numbered as follows: 1, 1, 2, 3, 4, 4, 4, 5, 5, 6, 6, and 6. If we take out one ball at random from the bag. What is the probability of drawing a ball numbered 1? There are possible outcomes for drawing 1, since there are two balls numbered 1. The total possible number of outcomes is 12, since there are 12 balls.
Thus the probability of drawing a 1 from the bag is the ratio 2/12 = 1/6 = .1667

2) A card is drawn from a pack of well shuffled 52 playing cards.

a) What is the total number of possible outcomes of this experiment?
There are 52 cards therefore there are 52 equally likely possible outcomes of this experiment.

b) What is the probability that the card is a black card?
There are 26 black cards in the pack out of 52 so the probability is 26/52 = 1/2 = 0.5

c) What is the probability that the card is a red ace?
There are two red aces, the ace of heart and the ace of diamond so the number of outcome of having a red ace is 2, and probability is 2/52 = 1/26.

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